The 1976 outbreak of Ebola virus disease in Zaire began in late August 1976. It was the second outbreak of Ebola, occurring shortly after the earlier 1976 outbreak in Sudan, and was the first known outbreak of Ebola. In total, 280 of the 318 cases of Ebola in Zaire resulted in death, a mortality rate of nearly 90%.

Lokela was initially diagnosed with malaria at the Yambuku Mission Hospital, and given quinine. However, Lokela returned to the mission hospital on 1 September with high fever.[3] Rest was recommended, and he returned home to his village of Yalikonde, about one kilometer from the mission complex. By 5 September, Lokela was in a critical condition with profuse bleeding from all orifices, vomiting, acute diarrhea, chest pains, headache, fever and in an agitated and confused state.[3] Lokela died shortly afterwards on 8 September.[4] On 28 August, a second man presented symptoms, claiming he was from the nearby village of Yandongi.[3] He left the hospital on the 30 August, as no clear cause could be identified from his symptoms, and was not seen again. On the same day, Yombe Ngongo, a patient at the hospital receiving treatment for anemia, checked out of the hospital and returned to her village. She soon fell seriously ill, and was tended to by her younger sister Euza. Yombe Ngongo died on 7 September, and her sister Euza soon followed on 9 September.[3]

Soon after Lokela's visit, a number of other cases were presented at the Yambuku Mission Hospital. A report from the World Health Organization (WHO) noted that "almost all subsequent infections had either received injections at the hospital or had had close contact with another case."[4] Shortly after family members prepared his body for burial, in accordance with local customs, 21 of Lokela's friends and relatives fell seriously ill and 18 later died.[3] The mission hospital's reuse of unsterilized needles also contributed to the spread of infection.[5]

Yambuku Mission Hospital was a remote Catholic hospital, and had no doctors and no laboratory facilities to aid in diagnosis.[3] Treatment was conducted by four Belgian nuns, a priest, one female nurse from Zaire and seven Zaireian males.[3] Urgent pleas for assistance were sent out on 12 September. On 15 September, the first doctor to arrive, Dr. Mgoi Mushola, prepared a report in which he noted that none of the many treatments provided met with success. He had inadvertently produced the first description of Ebola virus disease.[3]

The 1976 outbreak of Ebola occurred in Zaire, pictured in dark green, and additional cases occurred in present-day South Sudan, pictured in light green.

Peter Piot, a microbiologist and physician who investigated the ensuing epidemic, concluded that it was inadvertently caused by the Sisters of Yambuku Mission Hospital, who had given unnecessary vitamin injections to pregnant women in their prenatal clinic without sterilizing the needles and syringes.[6][7]

In all, 318 cases of Ebola were identified in Zaire, and 280 resulted in death. An additional 284 cases and 151 deaths occurred in nearby South Sudan. Yambuku Mission Hospital was closed after 11 of its 17 staff members died. Belgian nuns serving the community were also infected, and two of them died, along with Mayinga N'Seka, a Zairean nurse, after the group was transported to Kinshasa. With assistance from the WHO, the outbreak was eventually contained by quarantining local villagers in their communities, sterilizing medical equipment and providing protective clothing to medical personnel. The small Congolese Air Force provided helicopters to allow the outbreak team to visit 550 villages in the area.